In the preparation of ceramic products, it is customary to use as raw materials various forms of clay, shale, and the like. With the proliferation of electric power plants for generating electricity from coal there are generated substantial amounts of waste products, one of which is fly ash. Great effort has been made to find useful outlets for these coal waste products, in particular, fly ash. One of the uses for which coal fly ash has been recommended is for making ceramic and other construction materials.
Israeli Patents 61279 published Jul. 31, 1984 and 87143 published Nov. 21, 1991 (also published as U.S. Pat. No. 4,880,582, issued Nov. 14, 1989), disclose the use of small amounts of fly ash in building materials.
U.S. Pat. No. 2,576,565, issued Nov. 27, 1951 discloses ceramic products made from fly ash, slag and bentonite.
U.S. Pat. No. 3,679,441, issued Jul. 25, 1972 discloses ceramic products made from fly ash and plasticizer such as “Carbopol”.
U.S. Pat. No. 4,772,330, issued Sep. 20, 1988 describes a process for preparing a low water absorbing artificial lightweight aggregate using coal ash having a specific range of particle size and a hydraulic material.
EP 0222457, published May 20, 1987 (also published as U.S. Pat. No. 4,780,144, issued Oct. 25, 1988) discloses a method of producing a building element made form fly ash and Ca(OH)2 processed in a particular manner.